1. Field of the Invention
The present invention relates to a printed circuit board having a semiconductor package mounted on a printed wiring board, and a printed wiring board having a semiconductor package mounted thereon.
2. Description of the Related Art
In recent years, along with an increase in current consumption of a large-scale integration (hereinafter referred to as “LSI”) as a semiconductor package, a malfunction of the LSI caused by a power supply potential fluctuation has been a problem.
When the LSI operates, a potential fluctuation occurs, which is determined by the product of impedance of a power supply path between the LSI and a power supply circuit, and a current flowing on the power supply path. If a power supply potential fluctuation is large, a power supply voltage for driving the LSI becomes short so that a malfunction may occur. Further, the power supply potential fluctuation propagates to a cable or the like connected to a printed circuit board, and radiation noise is generated from the cable or the like as an antenna so as to cause a malfunction of peripheral electronic devices.
Therefore, it is required to reduce the power supply potential fluctuation of the LSI and to suppress the propagation thereof. As a technology to reduce the power supply potential fluctuation, there is a technology of reducing impedance of the power supply path for the LSI. In addition, as a technology to reduce the propagation of the power supply potential fluctuation, there is a decoupling technology of electrically decoupling in a high frequency range.
Conventionally, as a technology to reduce impedance of the power supply path for the LSI, there is known a technology of connecting power supply wirings in parallel between a semiconductor element in the LSI and power supply terminals by connecting multiple power supply terminals of the LSI to a main power supply pattern with multiple power supply patterns at multiple points (Japanese Patent Application Laid-Open No. 2001-119110). This parallel effect can reduce impedance of the power supply path for the LSI so as to reduce the power supply potential fluctuation. In Japanese Patent Application Laid-Open No. 2001-119110, the power supply pattern connected to the power supply circuit is disposed on a power supply layer disposed as an inner layer of the printed wiring board. In addition, on a surface layer of the printed wiring board, there is formed a power supply pattern for connecting multiple power supply terminals of the LSI to each other. The power supply pattern on the surface layer and the main power supply pattern on the inner layer are connected to each other using vias.
In recent years, multiple power supplies for the LSI have been used, and there is an LSI having multiple power supply terminal groups so as to support individual DC voltages. As for the printed wiring board on which this type of LSI is mounted, it is necessary to form multiple main power supply patterns to be applied with different DC voltages. On the other hand, in order to reduce cost, it is demanded to eliminate the power supply layer as the inner layer of the printed wiring board and to form the power supply patterns on the surface layer together with signal wiring patterns.
When the multiple power supply patterns extending from the multiple main power supply patterns applied with different DC voltages are formed for the multiple power supply terminals, it is necessary to form wirings so that the main power supply patterns do not cross each other to be short-circuited. As described in Japanese Patent Application Laid-Open No. 2001-119110, it is possible to form wirings so that the main power supply patterns do not cross each other to be short-circuited if the power supply layer for arranging the main power supply patterns is formed as the inner layer of the printed wiring board. However, if the power supply pattern is formed on the surface layer of the printed wiring board together with the signal wiring patterns, and if the power supply patterns are formed from surrounding regions of the LSI to the power supply terminals of the LSI, the power supply patterns always cross each other. Therefore, it is not possible to connect the power supply terminals of the LSI applied with different DC voltages to the power supply patterns on the surface layer. Therefore, it is not possible to reduce the number of layers of the printed wiring board.